Method and arrangement for determining the c-content in chemical processes

ABSTRACT

Continuous neutron activation analysis of a material undergoing chemical processing uses the intermittent bombardment of the material by a flux of neutrons of specific energy. The periods of bombardment alternate with periods of gamma ray analysis. The length of exposure time to the neutron flux and the time intervals between successive exposure periods, as well as the relation between these values and the half-life values of the nucleides are essential parameters in determining the carbon content of the material.

nited States Patent [191 Higatsberger et al.

METHOD AND ARRANGEMENT FOR DETERMINING THE C-CONTENT IN CHEMICAL PROCESSES Inventors: Michael J. Higatsberger, Graf.

Starhemberggasse 6/9, 1040 Vienna; Karl O. Rumpold, Freunbichlerweg 6, 1140 Vienna; Franz P. Viehbt'ick, Wiener Bruckstrasse 53, Maria, all of Austria Filed: Sept. 30, 1970 Appl. No.: 76,997

Foreign Application Priority Data Oct. 2, 1969 Austria .I 9314/69 U.S. Cl 250/395, 250/435 MR, 250/106 T Int. Cl. .l GZlh 5/02 Field of Search. 250/83.6 S, 83.6 W,'43.5 MR, 250/106 T, 83.3 R

[111 3,812,364 May 21, 1974 [56] References Cited UNITED STATES PATENTS 2,991,364 7/l96l Goodman 250/83.6 W X 3,025,399 3/[962 Verbinski.. 250/106 T X 3,025,400 3/1962 Schultz 250/106 T X Primary Examiner-Archie R. Borchelt Attorney, Agent, or FirmMcGlew and Tuttle 5 7] ABSTRACT Continuous neutron activation analysis of a material undergoing chemical processing uses the intermittent bombardment of the material by a flux of neutrons of specific energy. The periods of bombardment alternate with periods of gamma ray analysis. The length of exposure time to the neutron flux and the time intervals between successive exposure periods, as well as the relation between these values and the half-life values of the nucleides are essential parameters in determining the carbon content of the material.

7 Claims, 4 Drawing Figures 'FATEN'I'EUMAYZI 1914 SHEET 1 BF 2 .sec.)

FIGJ

FATENTED-MAYZI I974 FIGZ SUMMARY OF THE INVENTION The present invention relates to a method of, and apparatus for, determining the carbon content of a material undergoing chemical processing and, more particularly, for determining the carbon content in the production of steel.

A continuous analysis of the melt is especially desirable in the automatic processes of an LD steel mill. Traditionally, samples were drawn chiefly from the melts and routinely analyzed by a variety of methods with different measuring times and with different degrees of accuracy. A serious drawback of these methods is the time lag: it takes about five minutes to withdraw a sample and to perform the various analyses. It has therefore not been possible in the past to follow the process dynamically and to control it by immediate feedback.

By using neutron activation methods, with thermal neutrons from a reactor, for a prompt (my) analysis it has been mainly possible to determine exactly the presence of 1 percent to percent Manganese. However, this method cannot establish the presence of other elements such as Carbon, Silicon or Phosphorus in pig iron and steel because the effective cross sections of the respective nuclei are too small, as is evident from the following tables:

TABLE 1 Effective Pig iron cross-section Element Wt. in barn Activity in Fe 90.6 2.62 82.7447 Mn 4.0 13.3 17.2237 Si 1.0 0.16 0.0170 S 0.2 0.52 0.0094 P 0.2 0.0037 0.0015 Totals. 100.00 100.0000

TABLE 11 Effective Steel cross-section Element Wt. in barn Activity in Fe 95.8 2.62 91.0165 .Mn 2.0 13.3 8.9586 Si 1.0 1 0.16 0.0177 S 0.1 0.52 0.0048 F 0.1 0.2 0.0019 C 1.0 0.003 7 0.0004 Totals: 100.00 99.9999

' It is, therefore, an object of the present invention to overcome the drawbacks of prior art by providing a simple are reliable analytical method of, and apparatus for, determining the carbon content in material being chemically processed.

Another object is to provide an analytical method of and apparatus for, the determination of the carbon content or iron in the liquid state.

A further object is to determine the carbon content rapidly and on a continuing basis for immediate feedback in an automatic processing system.

Still another object is to eliminate from the (my) analysis of the material interfering radiation due to the neutron generator.

These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, by intermittently bombarding the material with neutrons of a predetermined energy. Capture of the neutrons by nuclei in the material which have an effective capture cross section results in many cases in the formation of radioactive nuclei which decay under emission of a gamma quantum. Table 111 shows a number of reactions resulting from the bombardment with neutrons of an energy of 14 Mev, the latter value referring to the energy of neutrons after leaving the neutron generator.

TABLE III N011- R tron Ptrod- Gamm 881C- energy 110 nu- 8118! y Element tion am Mev. clide Half-life in Me v.

F5 (11, 211) 0.015 14 Fe 8.9111 0.38 5.81% (11, p) 0. 373 14 Mn 291 (1 EC 0. s4 (11 a) 0.270 14 Cr 27.8 11 EC 0. 325 "{(nI211 0.5 14 Fe" 26 VEC 0.22 91.68% (11.11) 0.11 14 M11 25s 11 0.845 1.01; 2.13

Mn (1 ,211) 0.825 14 M11 291dEC 0.84 (11, p) 0.075 14 01 3.52 111 {(11, a) 0.05 14 v 3.75111144 11, 211 0.006 14 0 20.5111 98.89% (n, p) 0.019 14 B 002254.43

010 {(11,121) 0.08 14 Be Stable (11, p) 0.042 14 N16 7.1535 71,61 00.70% (11, a) 0.3 14 o Stable s1 (11, 1 0.25 14 .41 2.3m1.78 02.27% (11,11) 0.052 14 Mg Stable 11P (11, 211) 0.011 14 P50 2.6m 100% (11, 1) 0. 084 14 $1 2.0211

{(11,111) 0.15 14 A1 231111.78 (11, 1) 0.3 14 P32 14.30 05.02% (11, a) 0.109 14 s1 Stable It is seen from Table 111 that the reaction C (n,p)B with an effective capture cross-section of 19 millibam results in the formation of the short-lived boron isotope B which has a half-life of 0.021 sec and emits a gamma quantum of an energy of 4.43 Mev. Another re action 0 (r1,p)N", with an effective capture cross section of 42 millibarn yields the unstable isotope N with a half-life of 7.1 sec and which emits gamma quanta of energies of 6.13 and 7.13 Mev. Other (n,p) reactions of heavy nuclei yield radioisotopes of still longer half life, so that gamma ray activity of appreciable degree appears only after prolonged bombardment-with neutrons.

In one preferred embodiment of the invention, intermittent bombardment by neutrons is attained by alternatingly switching the neutron generator between an ON and an Off" position. The period during which the generator is in either position corresponds to the approximate half-life of 13'.

BRIEFDESCRIPTlON OF THE DRAWING FIG. 1 is a diagram showing the dependence of the bombardment products B and N on the lengths of the ON and OFF times of a neutron generator;

FIG. 2 is a diagram showing the number of B decompositions as a function of the ratio between the carbon pulses and the oxygen pulses;

FIG. 3 is a schematic representation of one embodiment of the invention; and

FIG. 4 is a schematic representation of another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is shown the relation between the radionucleides B and N and the On and Off time of a neutron generator, corresponding to periods of activation of the material. The dashed lines show the decay curves during the Off time of the generator. FIG. 1 represents data which were obtained when 5 X l n/cm /sec were directed onto kg of Fe (which includes about 50 g C). The iron was in the form of a disk which had a diameter of 16 cm and a thickness of 3 cm, (corresponding to the half-value of the range of 4.43 Mev gamma radiation). It is evident, from FIG. 1, that the number of radiating B and N nuclei increases with the On time of the neutron generator up to a saturation point. The saturation point for B lies beyond 1 sec., when the number of B atoms amounts to 1.4 X and for N it lies beyond 100 sec. when the number of N atoms is 0.8 X 10 The decay curve for B is a straight line on the semilogarithmic scale; for N which has a relatively long half-life the curve is an approximately straight line.

Sensible On and Off times for the generator are seen to lie in the range between I 100 milliseconds, and the operation of a pulsating neutron generator bears upon the number of the resulting B and N atoms exactly as shown by the curves of FIG. ll.

When the On time of the neutron generator is too long, (corresponding to a limit value for the curve in FIG. 1), the production of gamma-emitting B atoms is no longer profitable; moreover, during the prolonged On" period, too many N and heavier nuclei will be produced. When the On time of the generator is too short, the production of B atoms and consequently the carbon count will be too low. Conversely, if the Off time of the generator is too long, the count at the end of the suspended activation will be too low since the decay curve is an exponential function, as is well known. But if the Off time is too short the count will also be too low because in relation to the Off" time the On" time will predominate. Since the gamma radiation is measured only during the Off time, the measuring time per unit time becomes too short and hence, the intensity will be found to be too low.

The optimal On and Off times for a neutron generator are shown in FIG. 2, where the B emission, as a function of the ratio of the carbon pulses to the oxygen pulses is plotted against various values of On" and Off times. It was found that the coordinate point in FIG. 2 remains constant if On and Off" times are reversed. FIG. 2 also shows that the most appropriate On and Off times are, respectively, 20, 10, 5, or 0.1 milliseconds the values of the upper envelope of the family of curves of the figure. The yield is then about 6 X 10 pulses per minute or an average of 'IO pulses/sec of carbon alone over the entire solid angle.

Complete calculations have shown that this intensity does not vary during the operation. By contrast, the ratio of pulses of B to pulses of N deteriorates progressively during the operation, although it does not reach the critical value of about 0.6. Actually, the ratio will be more favorable, because the turbulence in the melt causes the radioactive N with a relatively long half-life to move to a lower region where it can be disregarded. It is, however, impossible to make a sensible estimate of the proportion, since one can hardly make any assumptions about the turbulence.

Subtracting, from the carbon value, an assumed factor for the solid angle and the efficiency of the gamma detector of about 10, the yield for carbon alone is 10 pulses/sec.

The illustration of FIG. 3 shows a crucible 1 containing a steel melt 2 whose carbon content is to be determined. A neutron collimator 3 spaced from the crucible 1 includes a tritium target 4 which is disposed at the apex of an angle formed by a pair of bores 5 and 7 which communicate with one another in the interior of the collimator. The target 4 is positioned in the interior of the bores 5, 7 at their junction. Bore 5 communicates at its end opposite the junction with bore 7, with a linear accelerator positioned outside the crucible l. Bore 7 defines a passage between the collimator 3 and the melt 2. The gamma radiation 9 which is produced by the reaction C (n,p)B and the subsequent B decay is intercepted by a detector 10 which is advantageously a semi-conductor or a scintillator detector. The best results have been obtained up to now with a Ge(li) semi-conductor detector.

The collimator 3 is preferably a spherical tank with a diameter of about 153 cm which is filled with water. When a stream of deuterium of about 2mA is issued from the linear accelerator 6 and passed through a tube 14 of about 8 cm diameter onto the tritium target 4, a neutron flux of about 10 n/sec with an energy of 14 Mev is emitted in accordance with the reaction l-I(d,n)He. The flux is emitted isotropically over the entire solid angle. Those neutrons 8 which pass through bore 7 arrive in the melt 2 without loss of the 14 Mev energy. The other neutrons resulting from the reaction are slowed down in the water of the collimator 3. When boron is added to the water the decelerated thermal neutrons are absorbed by the (ma) reaction of boron. The range of the alpha radiation which is produced is so short that the particles do not pass through the collimator tank 3 to the outside. The spherical collimator 3 further includes a recess (not designated) which forms a radiation shield for the oxygen lance 11 through which oxygen can be injected into the melt 2.

At 1 m distance from the collimator 3, the radiation level is only 0.2 percent of the value which, according to international radiation protection standards is admissible as a perfectly harmless yet maximum longterm dose.

In the embodiment of the invention shown in FIG. 4, the tritium target 4 and the detector 10 are immersed in the melt 2. The detector 10 is protected from the target 4 by shielding 13 which may include Li, H O, paraffin or graphite. The target 4 as well as the detector 13 are disposed in a tubular pipe 12. At its end distal from the melt 2 pipe 12 is connected to the linear accelerator 6 outside the crucible 1. The arrangement according to FIG. 4 is advantageous because of the satisfacof oxygen into the melt through the oxygen lance. If a measurement of the gamma radiation is required instead of process control, an appropriate measuring instrument, e.g., a multichannel pulse analyzer must be inserted in the electronic circuit. From the measured gamma radiation the carbon content of the material can be deduced by simple calculation.

While the determination of the carbon content in chemical processes may be carried out in a variety of materials, the method has been found to be particularly advantageous for the determination and control of processes involving iron in the liquid state.

What is claimed is:

l. A method of determining the carbon content of material used in the production of steel, comprising the steps of activating said material by bombardment with neutrons of predetermined energy in the range of about 12 to about 25 Mev; interspersing periods of predetermined length in the range of about 0.1 to about milliseconds during which said material is activated with periods of predetermined length during which activation of said material is suspended; measuring during said period of suspended activation the gamma radiation resulting from said activation of said material as the result of a C (n,p)B reaction; and deducing the carbon content of said material from said measured gamma radiation.

2. The method as defined in claim 1 comprising the step of selecting periods of activation and periods of suspended activation having a length of the order of magnitude of the half-life of B.

3. The method as defined in claim 1, comprising the step of selecting neutrons of 14 Mev energy for activation of said material.

4. The method as defined in claim 1, comprising the step of interspersing an activation period of 0.1 milliseconds with a period of suspended activation of 0.1 milliseconds.

5. The method as defined in claim 1, comprising the step of interspersing an activation period of 5 milliseconds with a period of suspended activation of 5 milliseconds.

6. The method as defined in claim 1 comprising the step of interspersing an activation period of 10 milliseconds with a period of suspended activation of 10 milliseconds.

7. The method as defined in claim 1, comprising the step of interspersing an activation period of 20 milliseconds. with a period of suspended activation of 20 milliseconds. 

2. The method as defined in claim 1 comprising the step of selecting periods of activation and periods of suspended activation having a length of the order of magnitude of the half-life of B12.
 3. The method as defined in claim 1, comprising the step of selecting neutrons of 14 Mev energy for activation of said material.
 4. The method as defined in claim 1, comprising the step of interspersing an activation period of 0.1 milliseconds with a period of suspended activation of 0.1 milliseconds.
 5. The method as defined in claim 1, comprising the sTep of interspersing an activation period of 5 milliseconds with a period of suspended activation of 5 milliseconds.
 6. The method as defined in claim 1 comprising the step of interspersing an activation period of 10 milliseconds with a period of suspended activation of 10 milliseconds.
 7. The method as defined in claim 1, comprising the step of interspersing an activation period of 20 milliseconds. with a period of suspended activation of 20 milliseconds. 